The 'best' conditions for doing this is when you have two angles... add them together and the difference between their total and 180 degrees is the magnitude of the remaining angle.
Otherwise, if you have one angle and the lengths of two sides you can use the sine rule.
This states that the length of each side, divided by the sine of the angle opposite it, is equal to the length of any other side, divided by the sine of the angle opposite it - or.....
a/sin A = b/sin B = c/sin C
Or, if you don't have a matching angle and side, you can use the cosine rule.
This says that
a2 = b2 + c2 - 2bc cosA
Now you have an angle and the side opposite it, and you can use the sine rule above.
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That will depend on the shape but if it's a triangle then the missing angle is 54 because there are 180 degrees in a triangle.
The two missing angles add up to 146 degrees. There's no way to tell what each of them is. In fact, any two angles that add to 146 can be used to construct a fine triangle.
180 minus two known angles = unknown angle
The sum of the angles in a triangle add up to 180. So in this case 180-35-25=120. The missing angle in this problem is 120 degrees.
Since the sum of the internal angles of a plane triangle is 180 degrees, the measure of the missing angle is 65 degrees. 180 - 74 - 41 = 65 degrees.